1. Field of the Invention
The present invention relates to a metallic porous body, which is usable as electrodes of electrochemical devices, such as batteries and capacitors, or as various filter materials.
2. Description of the Related Art
In the field of, for example, electric and electrochemical devices, such as capacitors and fuel batteries, two-dimensional or three-dimensional metallic porous bodies are used as electrode base materials. Similar metallic porous bodies are also used as materials of various filters, such as air filters and oil mist filters. Typical examples of such two-dimensional metallic porous bodies are, for example, pore-formed steel sheets, so-called “punching metals”, formed by punching metal sheets such as copper foils and steel sheets, and expand metals stretched and formed to a mesh state.
Typical example of three-dimensional metallic porous body includes foamed metals. Generally, the foamed metals are created by the steps of plating a metal such as nickel over urethan foam having lattice-state pores, sintering the plated formation in a reductant ambient, and removing the urethan foam. Fabric metals also can be fabricated in steps similar to the above, in which plating is performed over a non-woven fabric formed by knitting nylon or the like thin fibers.
For use as electrode base materials for electrochemical devices, such as batteries, porous bodies are required to be formed so as to easily extract electricity. Conventionally, three-dimensional metallic porous bodies such as foamed metals are generally used. However, three-dimensional metallic porous bodies are more costly because of using urethane, compared with two-dimensional metallic porous bodies. In addition, processing steps of sintering involves high fabrication costs. Furthermore, the three-dimensional metallic porous bodies require high strength by increasing the sizes of fibers and skeletons, resulting in increasing of weight, reducing in filling amount of active substances, and lowering capacity of batteries.
To solve the problems in a case where a three-dimensional metallic porous body of the type described above is used as an electrode base material, Patent Document 1 (Japanese Unexamined Patent Application Publication JP-9-265991,A (1997)) proposes that a base material with metallic fibers are attached on upper and lower portions of a metal sheet is used for an electric collector. Patent Document 2 (Japanese Unexamined Patent Application Publication JP-10-106580,A (1998)) proposes a manufacturing method in which a metal sheet for a base material is applied with a depressing pressure in an embossing process to provide burrs on individual apexes of concave and convex portions. Patent Document 3 (Japanese Unexamined Patent Application Publication JP-9-7603,A (1997)) proposes usage of a base material formed of a corrugated metal sheet.
However, in the case where a metal sheet is applied with a depressing pressure in an embossing process to form concave and convex portions and in the case where a metal sheet is corrugated, then burrs and sharp convex portions are likely to be formed on the surface of the base material. In addition, in the case of forming edged portions on the surface of the base material, it is difficult to finish the base-material fabrication with one processing step. In other words, the above case requires two or more processing steps of forming concave and convex portions and then forming burrs or corrugating. When machining steps are thus increased, the base material has accumulated strain and hence becomes liable to fracture, consequently leading to deterioration in the production yield. To prevent strain, an additional heat treatment process is required, thereby increasing the fabrication costs. Further, when fabricating a continuous base material, the base material should be wound. However, when the surface of the material has corrugations and/or edged protrusions, the material are likely to be hooked during winding, thereby leading to deterioration in the production yield. Concurrently, care needs to be taken when handling the fabricated base material.